163509

The second fastest way of getting the friends across takes 21 minutes.
The fastest takes 17 minutes. Can you work out how it is done?
2 (Ben) and 1 (Rachel) crosses first
Take 1 (Rachel) back over the bridge
Then take 7 (George) and 10 (Yvonne) over the bridge
Take 2 (Ben) back over the bridge.
1 (Rachel) and 2 (Ben) go over the bridge
Total time: 17 mins
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There are two optimal strategies for solving this type of problem:
Strategy 1 solves the original problem in 17 minutes
Strategy 2 solves the original problem in 21 minutes
Experiment with different speeds and work out when to use Strategy 1 and when to use Strategy 2.
Is there a way of determining which strategy will be best?
There is no way of determining which strategy is better unless you know the speeds of all the people
Can you find sets of speeds for which both strategies give the same crossing time?
Any set of speed where all numbers are the same gives off the time of 5 mins